非贯通球形空腔型轻质仿生结构的设计及其力学性能

为设计并开发轻量型仿生复合材料,分析了东方龙虱鞘翅断面的微观结构,发现龙虱鞘翅的内部空腔结构为非贯通球形空腔。受龙虱鞘翅独特结构的启发设计了一种轻质仿生结构,球形空腔以正六边形的形式分布于该结构内部。为考察该仿生结构的力学特性,引入了两种常见的中空结构,并借助有限元分析软件ANSYS分别对该仿生结构和其他两种常见的中空结构的压缩、拉伸及弯曲性能进行了有限元分析和对比研究。结果表明:该仿生结构较其他两种常见的中空结构具有更强的抗压能力、抗拉能力及更高的屈服强度,力学性能优异。该仿生结构在材料结构方面为研制新型仿生复合材料提供了仿生学参考。     

独角仙鞘翅微结构及其纳米力学性能

利用SEM对独角仙鞘翅的微结构进行了观测, 并借助纳米压痕仪测试分析了鞘翅的纳米力学性能。SEM试验表明独角仙鞘翅是一种具有拱形空腔的中空轻质生物复合材料, 其断面占空比为26.36%。鞘翅由外表皮和内表皮构成, 而内表皮又通过11~12层纤维层采用45°角正交叠加铺设, 层间辅以许多微纤维丝交叉连接方式编织在一起, 形成层合板结构。试验测得鞘翅外表皮纳米力学性能分别为: 硬度(0.28±0.13) GPa, 弹性模量(5.62±1.21) GPa, 接触刚度 (1.67±0.14)×10⁴ N/m。其纳米力学性能呈现拓扑分布规律, 由头部至尾部区域有增大趋势。试验测试结果为后续研究中设计一种基于独角仙鞘翅的新型轻质仿生结构提供了仿生学模型和理论参考。     

Crushing analysis and multi-objective optimization design for bionic thin-walled structure

Thin-walled structure has gained increasing attention and been widely used in the field of mechanical engineering due to their extraordinary energy absorption capacity and light weight. In this paper, we introduced a new energy absorbed structure named as bionic thin-walled structure (BTS) based on the structural characteristics of horsetails. In this study, six kinds of BTSs with different cross-sectional configurations under lateral loading conditions were investigated using nonlinear finite element method through LS-DYNA. According to the numerical results, it can be found that the cell number, inner wall diameter and wall thickness of the BTS had significant effect on the crashworthiness of the structure. In order to obtain the optimal design among the six kinds of BTSs, the six BTSs were optimized using a metamodel-based multi-objective optimization method which was developed by employing polynomial regression (PR) metamodel and multi-objective particle swarm optimization (MOPSO) algorithm. In the optimization process, we aimed to achieve maximum value of specific energy absorption (SEA) and minimum value of maximum impact force (MIF). Meanwhile, we also optimized the traditional thin-walled structures, i.e., the circular and square tubes. Based on the comparison of the Pareto fronts obtained by the multi-objective optimizations, we found that the crashworthiness of the BTSs was better than that of the circular and square tubes and the best BTS among the six kinds of BTSs was different when the limit of MIF was different. And, the optimal designs of the BTSs were found to have excellent energy absorption capacity under lateral impact and could be used in the future vehicle body.     

Improvement of energy absorption of impacted column due to transverse impact

The effect of a transverse impact on the buckling behavior of a column under axial impact loading was experimentally investigated. A column under an axial impact was subjected to a transverse impact to instantaneously reduce the structural stiffness. It was found that the absorption of the axial impact energy increased due to the post-buckling deformation being enlarged by transverse impact, though the axial impact load decreased. The experiment showed that the time elapsed from the beginning of the axial impact to the transverse impact significantly influenced the energy absorption. A transverse impact applied simultaneously with an axial impact produced the highest energy absorption. To compare the efficiency of the present method, tests without a transverse impact on specimens that had dents were also conducted. It was confirmed that the present method could increase the energy absorption without loosing any structural stiffness or static strength.     

型钢混凝土异形柱框架空间受力性能分析

为研究型钢混凝土异形柱框架的空间受力性能,对一个五层的双向两跨空间框架模型进行了低周反复加载试验,得到了空间框架的破坏形态及滞回曲线和骨架曲线,分析了其延性、位移角、刚度、耗能等抗震性能指标。基于此,采用OpenSees建立了空间框架的有限元模型,计算结果与试验结果吻合较好,进而对空间框架的破坏机制和协同工作机制进行了探讨,并分析了不同加载角下轴压比和柱肢长宽比对空间框架受力性能的影响。研究结果表明:型钢混凝土异形柱空间框架的梁端先于柱端发生破坏,节点损伤相对轻微,边框架的破坏程度比中框架严重;出铰顺序呈现为从梁端到柱端、从低层到高层、从中榀到边榀的发展规律;空间框架的滞回曲线基本对称且较为饱满,具有较好的延性及较强的耗能能力和抗倒塌能力,受力性能优于没有连接的独立框架;随着加载角的增大,空间框架的承载能力和耗能能力显著提高,初始刚度略微增大,延性先变好后变差;在相同加载角下,随着轴压比增大,空间框架的承载能力、延性和耗能能力均降低,初始刚度先增大后减小;随着柱肢长宽比增大,空间框架的承载能力、初始刚度和耗能能力均提高,延性变差。     

Investigating the nanomechanical properties and reversible color change properties of the beetle <Emphasis Type="Italic">Dynastes</Emphasis> <Emphasis Type="Italic">tityus</Emphasis>

The wing cases (elytra) of Dynastes tityus are able to change coloration from yellow-green in a dry state to deep brown in a wet state due to different degrees of water absorption. An environmental scanning electron microscope was used to investigate the elytra’s reversible color change properties. Because the elytra cuticle has a spongy structure that is composed of laminated chitin and protein, a UV–Vis–NIR spectrophotometer was used to investigate the elytra’s optical properties. The width of the curve peak gradually decreased from 60 to 10 nm when the color of the elytra varied from deep brown to yellow-green. In a humid environment, air between the voids was replaced by water with a higher refractive index that induced an elytra color changed from yellow-green to deep brown. Interestingly, when both humidity and elytra color changed, the elytra’s mechanical properties varied too. When the humidity of the environment changed from 100 to 34%, the reduced modulus (E _r) and hardness (H) of the elytra increased 230 and 440%, respectively. The storage modulus (E′) of the elytra is 1.98 ± 0.65 and 1.17 ± 0.22 GPa in yellow-green and deep brown color at 10 Hz, respectively, while their loss modulus (E″) is similar. tan δ of deep brown elytra is 0.072 ± 0.017, which is nearly two times higher than that of yellow-green. It can be demonstrated that when the elytra’s color turns to yellow-green, they are more elastic with less energy loss. The relationship between the elytra’s mechanical properties and structure color will not only help us gain insight into the biological functionality of the color change but also inspire the designs of artificial biomimetic devices.     

转盘式多足仿生机器人的运动学分析及优化

为解决多足机器人控制系统复杂、加工装配困难的问题,设计了一种基于单自由度Jansen连杆机构的转盘式多足仿生机器人,并对其进行运动学分析和优化。首先,运用旋量理论对机器人的单条仿生机械腿进行自由度验证,并运用复数矢量法对仿生机械腿进行运动学求解,得到其足端运动轨迹方程及各关节的转动角度。然后,基于仿生机械腿足端的运动轨迹及其影响因素,分析了其优化方向。接着,提出了转盘式传动机构,并对仿生机械腿的转动关节和足端进行了优化,同时利用SolidWorks软件对转盘式多足仿生机器人的步态进行了时序分析。最后,制作了转盘式多足仿生机器人样机并分析了其在常规路况下的运动能力,验证了其可行性。结果表明,改变曲柄长度和机架水平倾角可优化多足仿生机器人的运动轨迹,使其更符合实际应用所需;转盘式传动机构与多条仿生机械腿的叠加,提升了机器人的环境适应性。研究结果为后续机器人系统的设计及工程应用提供了重要的理论依据。     

Transferability of Charpy Absorbed Energy to Fracture Toughness Based on Weibull Stress Criterion

The relationship between Charpy absorbed energy and the fracture toughness by means of the (crack tip opening displacement (CTOD)) method was analyzed based on the Weibull stress criterion. The Charpy absorbed energy and the fracture toughness were measured for the SN490B steel under the ductile-brittle transition temperature region. For the instrumented Charpy impact test, the curves between the loading point displacement and the load against time were recorded. The critical Weibull stress was taken as a fracture controlled parameter, and it could not be affected by the specimen configuration and the loading pattern based on the local approach. The parameters controlled brittle fracture are obtained from the Charpy absorbed energy results, then the fracture toughness for the compact tension (CT) specimen is predicted. It is found that the results predicted are in good agreement with the experimental. The fracture toughness could be evaluated by the Charpy absorbed energy, because the local approach give     

Application of nano-indenter for investigation of the properties of the elytra cuticle of the dung beetle (Copris ochus Motschulsky)

The nanomechanical properties of the multilayer elytra cuticle of the dung beetle (Copris ochus Motschulsky) were investigated in the vertical and transverse directions using a nano-indenter. The reduced modulus Ev and hardness Hv of the surface cuticle in the vertical direction obtained by nano-indentation were 3.54+/-0.12 GPa and 0.20+/-0.01 GP, respectively. The nano-indentation result showed that the reduced modulus E(t) and hardness Ht of each layer were gradually reduced from the outer layer to the inner layer in the transverse direction. Ev was less than the largest Et presented at the outer layer (7.06+/-0.54 GPa). It was supposedly formed as a result of the composite effect of the multilayer. Without consideration of the anisotropy of chitin, an experimental model was proposed to describe the nanomechanical properties of the elytra cuticle.     

防撞击X型阻尼器及新型耗能减撞站房柱力学性能研究EI北大核心CSCD

针对易遭受撞击的站房结构柱等提出有效的防撞装置对结构安全运行至关重要,该文以此提出了一种新型耗能减撞站房柱,保障结构正常使用的同时达到最优耗能能力。采用LS-DYNA对新型耗能防撞设计的高铁站房结构柱进行防撞性能分析,并对其主要的耗能元件防撞击X型阻尼器和泡沫铝进行了研究。基于已有的经典试验进行数值模拟验证,包括钢板单向准静态加载试验、钢骨混凝土撞击试验和泡沫铝填充薄壁结构撞击试验。分析表明该文所建立的数值模型能够较好的模拟试验的撞击力和变形发展。以此建立防撞击X型阻尼器和新型耗能减撞站房柱的数值模型,从而优化单个防撞击X型阻尼器截面,使其耗能最好,并对比了不同因素下新型耗能减撞站房柱的吸能特性及加入泡沫铝后对新型耗能减撞站房柱的吸能影响。结果表明:在撞击荷载作用下,采用耗能最优防撞击X型阻尼器的新型耗能减撞站房柱中阻尼器将吸收97%的撞击能量,而内部结构柱中只有局部混凝土产生了裂缝;加泡沫铝的新型耗能减撞站房柱的吸能分布更加合理且吸能有较大的提升,但结构柱的塑性应变也会随之增加;整体而言,新型耗能减撞站房柱具有优良的吸能能力,保障了结构柱的安全。     

复合材料仿生高阶齿接结构承载特性及其影响因素

受自然骨缝连接结构的启发,基于图形分形原理,建立了不同阶次的复合材料仿生齿接结构模型。借助商用有限元软件ABAQUS,研究了齿接结构的界面损伤扩展规律与结构承载机制,分析了高阶齿接结构的结构互锁特性、齿数与齿型等因素对结构承载能力的影响。结果表明:高阶齿接结构的结构互锁特性极大地提高了结构承载能力并改变了结构损伤机制,适当增加单位宽度上的接齿数量与改变接齿局部特性可以降低应力集中,改善齿接结构力学性能。研究成果解释了自然骨缝连接结构在进化过程中所体现的力学原理,也为新型工程连接结构的发展开拓了新视野。      

Effect of loading history and material’s structural state on the yield onset of a polymethylmethacrylate

Constant strain rate tests at different rates and stress-relaxation tests at different intensities of the applied strain were performed on a polymethylmethacrylate under uniaxial loading conditions. Shear yielding onset was properly determined for each of the applied loading histories. Following previous works, different quantities were evaluated at the onset of yielding to identify a parameter, which could be fit for the definition of a yield criterion that takes into account the effect of the mechanical history. The influence of the material structural state on the parameters’ values at the onset of yielding was examined too.     

Computational modelling of irregular open‐cell foam behaviour under impact loading

Cellular structures represent an important class of engineering materials. Typical representative of such structures are metallic foams, which are being increasingly used in many advanced engineering applications due to their low specific weight, appropriate mechanical properties and excellent energy absorption capacity. For optimal design of cellular structures it is necessary to develop proper computational models for use in computational simulations of their behaviour under impact loading. The paper studies the effects of open‐cell metallic foam irregularity on deformation behaviour and impact energy absorption during impact loading by means of parametric computational simulations, using the lattice‐type modelling of open‐cell material structure. The 3D Voronoi technique is used for the reproduction of real, irregular open‐cell structure of metallic foams. The method uses as a reference a regular mesh structure and utilises an irregularity parameter to reproduce the irregularity of real open‐cell structure. A smoothing technique is introduced to assure proper stability and accuracy of explicit dynamic simulations using the produced lattice models. The effects of the smoothing technique were determined by comparative simulations of smoothed and unsmoothed lattices subjected to dynamic loading.     

甲虫生物材料的仿生研究进展

在经过长达百万年的进化过程中, 甲虫类生物材料形成了具有优异力学性能的优化的结构设计, 精巧而强韧的材料拓扑几何和满足多功能需求的表面结构, 成为当今材料仿生学新的研究对象之一。本文中从仿生学的角度出发, 对甲虫生物材料的微细结构、力学性能测试、功能形态学及材料几何构型拓扑等方面, 回顾了近年来国内外对甲虫的脚爪、鞘翅及飞行翅等甲虫生物材料的研究状况和进展, 并探讨了在各项研究中存在的问题及今后该领域的重点研究方向。      

东方龙虱鞘翅内表皮层及断面硬度和弹性模量

研究了东方龙虱去除外表皮后的鞘翅内表皮层及其鞘翅断面的力学性能。利用纳米压痕仪测得鞘翅内表皮层硬度和弹性模量分别为(0.065±0.007) GPa和(0.704±0.013) GPa, 均远远小于鞘翅外表皮层的硬度和弹性模量。鞘翅断面的力学性能测试结果表明: 在鞘翅横断面上, 靠近联接部位的硬度和弹性模量略大于鞘翅中部和外侧; 而在鞘翅纵向断面上, 鞘翅中部的硬度和弹性模量明显大于头部和尾部, 其断面力学性能呈现一定的分布规律。      

四种甲虫鞘翅的力学参数测定及微结构观测

研究了4种甲虫(白星花金龟、 东方龙虱、 独角仙、 毛黄鳃金龟)鞘翅的材料力学参数及其微结构。鞘翅截面微观结构观察表明, 这4种甲虫鞘翅均由鞘翅背壁、 中空夹芯层和鞘翅腹壁构成, 背、 腹壁之间由桥墩状几丁质纤维空心柱体结构连接, 两鞘翅间以凹凸啮合结构联接。用纳米压痕仪测得这4种甲虫鞘翅背壁致密层的弹性模量均值分别为9.08、 8.21、 4.76、 6.00GPa, 硬度分别为0.44、 0.48、 0.18、 0.18GPa。用多功能材料性能实验机测定白星花金龟、 东方龙虱、 独角仙鞘翅之间的联接强度分别为46.43、 7.38、 11.34mN/mm。该研究为轻质结构的设计提供了仿生学基础。      

Some observations on the dynamic elastic-plastic buckling of a structural model

The use of a simple imperfection-sensitive elastic-plastic model for studying the non-linear buckling of short columns and cylndrical shells under dynamic axial compression is discussed in this paper. The axial impact loading of the model by a mass with an initial velocity is considered as a particular example. The critical impact velocities are determined for wholly elastic and elastic-plastic materials with linear strain hardening characteristics. The results show that the maximum initial kinetic energy at the transition between stable and unstable behaviour after impact is sensitive to the magnitude of the material strain hardening parameter. It is also evident from the results that impact due to larger masses leads to larger lateral displacements at buckling and that the instability of a column is more sensitive to the presence of initial imperfections at higher impact velocities. Some guidance is offered on the choice of the various parameters in the idealized model for the analysis of practical engineering structures.     

锈蚀钢框架柱抗震性能试验研究及有限元分析

为深入研究锈蚀钢框架柱的抗震性能,通过改变加载制度和轴压比,对6榀相同锈蚀程度的钢框架柱进行了低周往复加载试验,观察其受力过程和破坏形态,分析了不同加载制度和轴压比对锈蚀钢框架柱的滞回曲线、骨架曲线、强度和刚度退化、耗能能力等抗震性能的影响。并采用通用软件ABAQUS对试验框架柱进行了非线性有限元分析。结果表明:有限元分析结果与试验结果吻合较好,试件均发生延性较好的破坏,其滞回曲线也较为饱满,表现出良好的耗能能力和延性;加载路径对试件的塑性发展与耗能能力有较大影响;随着轴压比的增大,试件极限承载力和耗能能力降低,强度和刚度退化加快。     

Evaluation on Fracture Toughness at Dynamic Loading for Welded Joint Based on the Local Approach

The changes in mechanical properties and fracture toughness by dynamic loading were investigated with experiments. The parameter R, which can reflect the effect of the loading rate and the temperature rising during the high loading rate, could be employed to describe the constituent relation for the typical structure steel and its weld metal. The dynamic loading effect on the stress/strain fields and the temperature variation in the vicinity of the crack tip was analyzed by the finite element method, the dynamic fracture behavior was evaluated based on the local approach. It has been found that the Weibull stress is an effective fracture parameter, independent of the temperature and the loading rate.     

SIZE EFFECTS ON IMPACT RESPONSE OF COMPOSITE LAMINATES

Delamination was known to be one of the most important damage modes in composite laminates subjected to impact loading. In an effort to further understand the impact response of composite laminates, various degrees of impact ranging from subperforation to perforation were introduced to glass/epoxy laminates through an instrumented drop-weight impactor. In addition, composite laminates of various in-plane dimensions and thicknesses were examined for in-plane dimensional and thickness effects, respectively. Experimental results showed that in-plane dimensional effect was not as significant as thickness effect. The impacted composite laminates were then subjected to compression after impact (CAI) tests for characterizations of residual mechanical properties. Experimental results showed that perforation was the most important damage stage in composite laminates subjected to impact loading since impact characteristics (peak force, contact duration and absorbed energy) and mechanical properties degradation (residual compressive maximum force and residual compressive absorbed energy) of composite laminates became stable once perforation took place. However, it was also found that delamination played a very important role in the characterizations of mechanical properties degradation. Since the impact response of composite laminates is due to plate bending to some extent, bending analysis was used to explain the greater influence of thickness effect to in-plane dimensional effect. It was also found that bending analysis was feasible for interpretation of delamination in mechanical properties degradation.